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geekpi
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[#]: subject: "A look inside an EPUB file"
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[#]: via: "https://opensource.com/article/22/8/epub-file"
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[#]: author: "Jim Hall https://opensource.com/users/jim-hall"
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[#]: collector: "lkxed"
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[#]: translator: "geekpi"
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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A look inside an EPUB file
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======
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EPUB files are a great way to publish content using an open format.
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![How to find files in Linux][1]
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Image by: Lewis Cowles, CC BY-SA 4.0
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eBooks provide a great way to read books, magazines, and other content on the go. Readers can enjoy eBooks to pass the time during long flights and train rides. The most popular eBook file format is the EPUB file, short for "electronic publication." EPUB files are supported across a variety of eReaders and are effectively the standard for eBook publication today.
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The EPUB file format is an open standard based on XHTML for content and XML for metadata, contained in a zip file archive. And because everything is based on open standards, we can use common tools to create or examine EPUB files. Let's explore an EPUB file to learn more about it. [A guide to tips and tricks for C programming][2], published earlier this year on Opensource.com, is available in PDF or EPUB format.
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Because EPUB files are XHTML content and XML metadata in a zip file, you can start with the `unzip` command to examine the EPUB from the command line:
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```
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$ unzip -l osdc_Jim-Hall_C-Programming-Tips.epub
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Archive: osdc_Jim-Hall_C-Programming-Tips.epub
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Length Date Time Name
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--------- ---------- ----- ----
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20 06-23-2022 00:20 mimetype
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8259 06-23-2022 00:20 OEBPS/styles/stylesheet.css
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1659 06-23-2022 00:20 OEBPS/toc.xhtml
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4460 06-23-2022 00:20 OEBPS/content.opf
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44157 06-23-2022 00:20 OEBPS/sections/section0018.xhtml
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1242 06-23-2022 00:20 OEBPS/sections/section0002.xhtml
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22429 06-23-2022 00:20 OEBPS/sections/section0008.xhtml
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[...]
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9628 06-23-2022 00:20 OEBPS/sections/section0016.xhtml
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748 06-23-2022 00:20 OEBPS/sections/section0001.xhtml
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3370 06-23-2022 00:20 OEBPS/toc.ncx
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8308 06-23-2022 00:21 OEBPS/images/image0011.png
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6598 06-23-2022 00:21 OEBPS/images/image0009.png
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[...]
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14492 06-23-2022 00:21 OEBPS/images/image0005.png
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239 06-23-2022 00:20 META-INF/container.xml
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--------- -------
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959201 41 files
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```
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This EPUB contains a lot of files, but much of this is content. To understand how an EPUB file is put together, follow the process flow of an eBook reader:
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1. eBook readers need to verify that the EPUB file is really an EPUB file. They verify the file by examining the `mimetype` file at the root of the EPUB archive. This file contains just one line that describes the MIME type of the EPUB file:
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```
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application/epub+zip
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```
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2. To locate the content, eBook readers start with the `META-INF/container.xml` file. This is a brief XML document that indicates where to find the content. For this EPUB file, the `container.xml` file looks like this:
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```
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<?xml version="1.0" encoding="UTF-8"?>
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<container version="1.0" xmlns="urn:oasis:names:tc:opendocument:xmlns:container">
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<rootfiles>
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<rootfile full-path="OEBPS/content.opf" media-type="application/oebps-package+xml"/>
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</rootfiles>
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</container>
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```
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To make the `container.xml` file easier to read, I split the single line into multiple lines and added some spacing to indent each line. XML files don't really care about extra white space like new lines and spaces, so this extra spacing doesn't affect the XML file.
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3. The `container.xml` file says the root of the EPUB starts with the `content.opf` file in the OEBPS directory. The OPF extension is because EPUB is based on the Open Packaging Format, but the `content.opf` file is really just another XML file.
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4. The `content.opf` file contains a complete manifest of the EPUB contents, plus an ordered table of contents, with references to find each chapter or section. The `content.opf` file for this EPUB is quite long, so I'll show just a bit of it here as an example.
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The XML data is contained within a `<package>` block, which itself has a `<metadata>`block, the `<manifest>` data, and a `<spine>`block that contains the eBook's table of contents:
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```
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<?xml version="1.0" encoding="UTF-8"?>
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<package unique-identifier="unique-identifier" version="3.0" xmlns="http://www.idpf.org/2007/opf" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:dcterms="http://purl.org/dc/terms/" xmlns:opf="http://www.idpf.org/2007/opf">
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<metadata>
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<dc:identifier id="unique-identifier">osdc002</dc:identifier>
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<dc:title>Tips and Tricks for C Programming</dc:title>
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<dc:creator>Jim Hall</dc:creator>
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<dc:language>English</dc:language>
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<meta property="dcterms:modified">2022-06-23T12:09:13Z</meta>
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<meta content="LibreOffice/7.3.0.3$Linux_X86_64 LibreOffice_project/0f246aa12d0eee4a0f7adcefbf7c878fc2238db3 (libepubgen/0.1.1)" name="generator"/>
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</metadata>
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<manifest>
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...
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<item href="sections/section0001.xhtml" id="section0001" media-type="application/xhtml+xml"/>
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<item href="images/image0003.png" id="image0003" media-type="image/png"/>
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<item href="styles/stylesheet.css" id="stylesheet.css" media-type="text/css"/>
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<item href="toc.ncx" id="toc.ncx" media-type="application/x-dtbncx+xml"/>
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...
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</manifest>
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<spine toc="toc.ncx">
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<itemref idref="section0001"/>
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<itemref idref="section0002"/>
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<itemref idref="section0003"/>
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...
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</spine>
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</package>
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```
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You can match up the data to see where to find each section. That’s how EPUB readers do it. For example, the first item in the table of contents references `section0001` which is defined in the manifest as located in the `sections/section0001.xhtml` file. The file doesn’t need to be named the same as the idref entry, but that’s how LibreOffice Writer’s automated process created the file. (You can see in the metadata that this EPUB was created with LibreOffice version 7.3.0.3 on Linux, which can export content as EPUB files.)
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### The EPUB format
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EPUB files are a great way to publish content using an open format. The EPUB file format is XML metadata with XHTML content, inside a zip container. While most technical writers use tools to create EPUB files, because EPUB is based on open standards means you can create your own EPUB files in some other way.
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/22/8/epub-file
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作者：[Jim Hall][a]
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选题：[lkxed][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/jim-hall
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[b]: https://github.com/lkxed
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[1]: https://opensource.com/sites/default/files/lead-images/find-file-linux-code_magnifying_glass_zero.png
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[2]: https://opensource.com/downloads/guide-c-programming
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123
translated/tech/20220816 A look inside an EPUB file.md
Normal file
123
translated/tech/20220816 A look inside an EPUB file.md
Normal file
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[#]: subject: "A look inside an EPUB file"
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[#]: via: "https://opensource.com/article/22/8/epub-file"
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[#]: author: "Jim Hall https://opensource.com/users/jim-hall"
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[#]: collector: "lkxed"
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[#]: translator: "geekpi"
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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深入了解 EPUB 文件
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======
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EPUB 文件是使用开放格式发布内容的好方法。
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![How to find files in Linux][1]
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图片来源：Lewis Cowles，CC BY-SA 4.0
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电子书提供了一种随时随地阅读书籍、杂志和其他内容的好方法。读者可以在长途飞行和乘坐火车时享受电子书打发时间。最流行的电子书文件格式是 EPUB 文件，是“电子出版物”的缩写。 EPUB 文件受到各种电子阅读器的支持，并且是当今电子书出版的有效标准。
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EPUB 文件格式是基于 XHTML 内容和 XML 元数据的开放标准，包含在 zip 存档中。由于一切都基于开放标准，我们可以使用通用工具来创建或检查 EPUB 文件。让我们探索一个 EPUB 文件以了解更多信息。 [C 编程技巧和窍门指南][2]，于今年早些时候在 Opensource.com 上发布，提供 PDF 或 EPUB 格式。
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因为 EPUB 文件是 zip 文件中的 XHTML 内容和 XML 元数据，所以你可以用 `unzip` 命令在命令行检查 EPUB：
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```
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$ unzip -l osdc_Jim-Hall_C-Programming-Tips.epub
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Archive: osdc_Jim-Hall_C-Programming-Tips.epub
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Length Date Time Name
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--------- ---------- ----- ----
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20 06-23-2022 00:20 mimetype
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8259 06-23-2022 00:20 OEBPS/styles/stylesheet.css
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1659 06-23-2022 00:20 OEBPS/toc.xhtml
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4460 06-23-2022 00:20 OEBPS/content.opf
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44157 06-23-2022 00:20 OEBPS/sections/section0018.xhtml
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1242 06-23-2022 00:20 OEBPS/sections/section0002.xhtml
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22429 06-23-2022 00:20 OEBPS/sections/section0008.xhtml
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[...]
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9628 06-23-2022 00:20 OEBPS/sections/section0016.xhtml
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748 06-23-2022 00:20 OEBPS/sections/section0001.xhtml
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3370 06-23-2022 00:20 OEBPS/toc.ncx
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8308 06-23-2022 00:21 OEBPS/images/image0011.png
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6598 06-23-2022 00:21 OEBPS/images/image0009.png
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[...]
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14492 06-23-2022 00:21 OEBPS/images/image0005.png
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239 06-23-2022 00:20 META-INF/container.xml
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--------- -------
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959201 41 files
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```
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这个 EPUB 包含很多文件，但其中大部分是内容。要了解 EPUB 文件是如何组合在一起的，请遵循电子书阅读器的流程：
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1. 电子书阅读器需要验证 EPUB 文件是否真的是 EPUB 文件。他们通过检查 EPUB 存档根目录中的 `mimetype` 文件来验证文件。该文件仅包含一行描述 EPUB 文件的 MIME 类型：
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```
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application/epub+zip
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```
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2. 为了定位内容，电子书阅读器从 `META-INF/container.xml` 文件开始。这是一个简短的 XML 文档，指示在哪里可以找到内容。对于此 EPUB 文件，`container.xml` 文件如下所示：
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```
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<?xml version="1.0" encoding="UTF-8"?>
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<container version="1.0" xmlns="urn:oasis:names:tc:opendocument:xmlns:container">
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<rootfiles>
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<rootfile full-path="OEBPS/content.opf" media-type="application/oebps-package+xml"/>
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</rootfiles>
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</container>
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```
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为了使 `container.xml` 文件更易于阅读，我将单行拆分为多行，并添加了一些间距来缩进每行。 XML 文件并不真正关心新行和空格等额外的空白，因此这种额外的间距不会影响 XML 文件。
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3. `container.xml` 文件表示 EPUB 的根目录以 OEBPS 目录中的 `content.opf` 文件开头。 OPF 扩展是因为 EPUB 基于 Open Packaging Format，但 `content.opf` 文件实际上只是另一个 XML 文件。
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4. `content.opf` 文件包含一个完整的 EPUB 内容清单，以及一个有序的目录，以及查找每一章或每一节的参考。这个 EPUB 的 `content.opf` 文件很长，因此我将在此仅展示一小部分作为示例。
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XML 数据包含在 `<package>` 块中，该块本身具有 `<metadata>` 块、`<manifest>` 数据和包含电子书目录的 `<spine>` 块：
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```
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<?xml version="1.0" encoding="UTF-8"?>
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<package unique-identifier="unique-identifier" version="3.0" xmlns="http://www.idpf.org/2007/opf" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:dcterms="http://purl.org/dc/terms/" xmlns:opf="http://www.idpf.org/2007/opf">
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<metadata>
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<dc:identifier id="unique-identifier">osdc002</dc:identifier>
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<dc:title>Tips and Tricks for C Programming</dc:title>
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<dc:creator>Jim Hall</dc:creator>
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<dc:language>English</dc:language>
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<meta property="dcterms:modified">2022-06-23T12:09:13Z</meta>
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<meta content="LibreOffice/7.3.0.3$Linux_X86_64 LibreOffice_project/0f246aa12d0eee4a0f7adcefbf7c878fc2238db3 (libepubgen/0.1.1)" name="generator"/>
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</metadata>
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<manifest>
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...
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<item href="sections/section0001.xhtml" id="section0001" media-type="application/xhtml+xml"/>
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<item href="images/image0003.png" id="image0003" media-type="image/png"/>
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<item href="styles/stylesheet.css" id="stylesheet.css" media-type="text/css"/>
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<item href="toc.ncx" id="toc.ncx" media-type="application/x-dtbncx+xml"/>
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...
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</manifest>
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<spine toc="toc.ncx">
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<itemref idref="section0001"/>
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<itemref idref="section0002"/>
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<itemref idref="section0003"/>
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...
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</spine>
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</package>
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```
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你可以把数据匹配起来，看看在哪里可以找到每个部分。EPUB 阅读器就是这样做的。例如，目录中的第一项引用了 `section0001`，它在清单中被定义为位于 `sections/section0001.xhtml` 文件中。该文件的名称不需要与 idref 条目相同，但 LibreOffice Writer 的自动程序就是这样创建该文件的。(你可以在元数据中看到，这个 EPUB 是在 Linux 上用 LibreOffice 7.3.0.3 版本创建的，它可以将内容导出为EPUB文件。)
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### EPUB 格式
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EPUB 文件是一种使用开放格式发布内容的好方法。EPUB 文件格式是 XML 元数据与 XHTML 内容，包含在一个 zip 文件内。虽然大多数技术作家使用工具来创建 EPUB 文件，因为 EPUB 是基于开放标准，意味着你可以使用其他方式创建自己的 EPUB 文件。
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/22/8/epub-file
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作者：[Jim Hall][a]
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选题：[lkxed][b]
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译者：[geekpi](https://github.com/geekpi)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/jim-hall
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[b]: https://github.com/lkxed
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[1]: https://opensource.com/sites/default/files/lead-images/find-file-linux-code_magnifying_glass_zero.png
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[2]: https://opensource.com/downloads/guide-c-programming
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